1. Field of the Invention
Apparatuses and methods consistent with the present invention relate generally to ad-hoc networks and packet transmissions therein, and more particularly, to ad-hoc networks wherein packets are transmitted to a plurality of target regions.
2. Description of the Related Art
A typical mobile communication system delivers data between a mobile element and a base station. The mobile element and the base station directly transmit and receive data without the data passing through any other mobile elements or nodes. In comparison, to carry packets from a source node to a destination node in an ad-hoc sensor network, the packets are directly transmitted to the destination node without using an existing infra-network. In this situation, if the destination node is not adjacent to the source node, but is instead distanced by several hops from the source node, the packets are delivered via intermediate nodes. Other nodes can be used to geocast packets from a source node to a specific region over the ad-hoc sensor network. The geocasting floods packets to nodes located in a targeted geographical region. The targeted geographical region is referred to as a target region. In the following, descriptions are made on how a source node in an ad-hoc network transmits packets to a target region.
FIG. 1 illustrates how to transmit packets to a conventional target region. In FIG. 1, the ad-hoc network is established with a plurality of nodes including a source node. A target region covering nodes that are to receive packets from the source node is defined within the ad-hoc network.
It is assumed that the plurality of the nodes including the source node in the ad-hoc network know their own IDs and location information, location information of the target region, and location information of one-hop neighbor nodes. The source node, which is aware of the location information of the target region, transmits the packets containing the location information of the target region, to the nearest neighbor node from the target region. Nodes receiving the packets determine whether they are located in the target region based on the location information of the target region contained in the packets. When the nodes receiving the packets do not have information as to a neighbor node nearer to the target region than themselves, the nodes determine that they are the destination of the packets and broadcast the received packets over a specified area based on the location information of the target region. Conversely, when the nodes have information of a neighbor node nearer to the target region, the nodes forward the received packets to the discovered neighbor node. As such, the packets originating from the source node can be delivered to the specified target region and flooded to the nodes therein.
Particularly, the source node transmits generated packets toward a neighbor node estimated to be the nearest node to the target region, and the packets are received at one-hop nodes (i.e., nodes adjacent to the source node by one hop). The one-hop nodes from the source node compare location information of the target region contained in the received packets with their own location information. If the location information of the target region matches their location information, or, if there is no other neighbor node determined to be nearer to the target region based on location information of their known neighbor nodes, the one-hop nodes determine that they are located in the target region and broadcast the packets over the target region. Conversely, if there is another neighbor node nearer to the target region, the one-hop nodes forward the packet to the discovered node. By repeating the above procedure, the transmission route from the source node to the target region can be established.
The plurality of nodes in the ad-hoc network can obtain IDs and location information of neighbor nodes. Generally, nodes in the ad-hoc network have guaranteed mobility. Hence, the nodes transmit and receive packets to and from neighbor nodes periodically and, thus, update information relating to the neighbor nodes.
As for a plurality of target regions to which the same packets are to be delivered, the conventional ad-hoc network delivers the packets to the target regions as illustrated in FIG. 1. FIG. 2 depicts a conventional packet transmission method in relation to a plurality of target regions. In FIG. 2, the ad-hoc network includes a target region A and a target region B. A source node transmits the same packets to the target regions A and B, respectively, along different routes according to the conventional packet transmission method.
When packets are transmitted to the plurality of target regions along the different routes, excess overhead may be incurred and the packet transmission between the source node and the target regions may be delayed. In addition, as the transmission distance is extended, the packet transmission results in a waste of power used for transmitting the packet, which is inefficient.